feat: Add cutout schema version

[euronion]

This PR adds a cutout data schema version to all cutouts created by atlite.
Having a cutout schema version allows us to define breaking changes between atlite versions for cutouts.
It also allows us to define a migration logic (if migration is possible).

Note: Migrating cutouts between versions does not guarantee that cutouts with the same schema version are identical - changes in processing by atlite as well as in upstream data can happen independently of the schema version.

The schema version is an integer value that is bumped whenever the schema changes.
Simple changes to the schema may be migrated, more complex changes may make different schema versions incompatible with each other.

Checklist

• Code changes are sufficiently documented; i.e. new functions contain docstrings and further explanations may be given in doc.
• Unit tests for new features were added (if applicable).
• [n/a] Newly introduced dependencies are added to environment.yaml, environment_docs.yaml and setup.py (if applicable).
• A note for the release notes doc/release_notes.rst of the upcoming release is included.
• I consent to the release of this PR's code under the MIT license.